It has long been known that the unique crystalline structure of graphite makes it anisotropic with respect to conducting electrons. Its structure basically comprises planes of aromatically bound carbon atoms. Hence, each of such planes has .pi. clouds of electrons above and below it. These electron clouds have been said to contribute to its anisotropic conductive behavior, the conductivity being in a direction parallel to the aromatic carbon planes. This conductivity is approximately 5 percent that of copper.
It also has been known that certain elements or molecules, when diffused into the graphite lattice, assume positions interstitial to the aromatic planes and improve graphite conductivity. Ubbeholde, for example, found that the interstitial compound formed between graphite and nitric acid has a conductivity almost equal to that of copper (which is 0.6.times.10.sup.6 ohms.sup.-1 cm..sup.-1) when measured parallel to the aromatic planes [A. R. Ubbeholde, Proc. Roy. Soc., A304, 25, (1968)].
U.S. Pat. No. 3,409,563 describes conductive graphite structures formulated from vermicular graphite and an agent such as Br.sub.2, FeCl.sub.3, CrO.sub.2 Cl.sub.2, SO.sub.3, SbCl.sub.5, CrCl.sub.3, ICl, CrO.sub.3, AuCl.sub.3, InCl.sub.3, PtCl.sub.4, CrO.sub.2 F.sub.2, TaCl.sub.5, SmCl.sub.3, ZrCl.sub.4, UCl.sub.4, and YCl.sub.3. The treated vermicular graphite is then compressed into structures.
German Pat. No. 2,537,272 discloses the formation of an electrically conductive graphite intercalation compound employing a strong acid halide system wherein graphite is reacted with "the proton donor (Bronsted acid), hydrogen fluoride, and an electron acceptor (Lewis acid) such as boron trihalide, a tetrahalide from a Group IV metal, or a pentahalide from a Group V metal."
It has been reported that sulfur trioxide alone will intercalate graphite. See, for instance, C.R. Acad. Sci. Paris, Vol. 262, pages 1074 to 1075 (1966) by Michele Bogouin, Herve Fuzellier and Albert Herold.
Additionally, it has been reported that a mixture of sulfur acid and sulfur trioxide will intercalate graphite and thereby increase its electrical conductivity. See, for instance, Physica, Vol. 99B, pages 541 to 546 (1980) by E. McRae, A. Metrot, P. Willmann and A. Herold.
In U.S. Pat. No. 4,293,450 is disclosed the intercalation of graphite with (a) fluorosulfonic acid, chlorosulfonic acid, or mixtures thereof, and (b) a boron trihalide, a tetrahalide of a Group IV element, a pentahalide of a Group V element, or mixtures thereof. This disclosure is silent concerning how the desired intercalation could be aided through the presence of another reactant such as that claimed herein.
In commonly assigned U.S. Pat. No. 4,388,227 and U.S. Ser. No. 445,758, filed Nov. 30, 1982, is described an improved carbonaceous fibrous material comprising graphitic carbon which has been found to be particularly suited for intercalation.
It is an object of the present invention to provide an improved process for forming an intercalated electrically conducting composition.
It is another object of the present invention to provide an improved process whereby graphite is intercalated at an increased rate and possibly a greater electrical conductivity is achieved in the final intercalated product.
It is another object of the present invention to form an intercalated graphite product of maximum conductance within a minimum amount of time.
It is a further object of the present invention to provide an improved process for the intercalation of graphite which can be carried out on a relatively economical basis with the need to employ only small amounts of relatively expensive intercalant.
These and other objects, as well as the scope, nature, and utilization of the claimed invention will be apparent to those skilled in the art from the following detailed description and appended claims.